Greek philosophy in the archaic era is quite different from Greek philosophy in classical era. What are the differences? What caused the changes?
In the archaic era, the pre-Socratic philosophers lived largely outside of Greece in the Greek-speaking Mediterranean colonies. They were interested in topics related to physics, astronomy, mathematics, biology, and chemistry. They came from a comfortable middle-class or merchant class, having leisure time to think about such topics. Living away from mainland Greece, they were more adventurous in personality, corresponding to the frontier nature of their surroundings. They were optimistic, because the colonies abounded with financial and political opportunities.
During the classical era, the philosophers lived mainly in Greece itself. While retaining interests in physics and metaphysics, they were very interested in social and ethical questions. They were men of less influence and less wealth.
Certain factors in Greek society may have caused philosophers to focus more on political and moral questions: the Peloponnesian War, begun because of Athenian greed, and carried out under pretentious propaganda, weakened Greece and removed optimism. The fabled democratic government of Athens turned out to be, in reality, a system of bribery and extortion, leading to incidents such as the death of Socrates. Greek heroes, like Themistocles, revealed themselves to be savage and brutal, capable of atrocities. (Remember that Themistocles engaged in human sacrifice on the evening before the Battle of Salamis to ensure his victory.) Small wonder that someone like Plato would write a detailed discussion of the question: what is justice?